The present invention relates to circuit arrangements for reducing current drain of batteries and, more particularly, to such arrangements in which the drain reduction is initiated by a potentiometer.
In many electronic circuits the supply of electrical power available is just that of a battery which is subject to a relatively short life if the circuit supplied thereby draws significant current over substantial periods of time. In battery operated equipment, not only is minimizing power dissipation important to lengthen the life of the battery, but this must often be done with circuit arrangements operating from a low voltage.
A typical example of equipment where these conditions exist is hearing aids as shown in electrical schematic diagram form in FIG. 1 having a microphone, 10, a preliminary amplifier, 11, an output amplifier, 12, (shown with a solid line output for a single polarity output signal and with an added dashed line of alternating long and short dashes for a double polarity output signal for which also the speaker ground connection would be eliminated), a speaker or receiver, 13, a battery voltage supply terminal, 14, between which and the ground reference voltage there is a voltage regulator, 15. Voltage regulator 15 is shown providing regulated voltage to microphone 10 and two regulated voltages of different values to preliminary amplifier 11 and output amplifier 12 which also receive battery voltage. Preliminary amplifier 11 and output amplifier 12 have a volume control potentiometer, 16, between them with the mechanically operated wiper ganged (as shown by the dashed line provided using long dashes) to an on/off switch, 17, controlling application of electrical voltage to the hearing aid circuit. A capacitor, 18, prevents constant voltages in either microphone 10 or preliminary amplifier 11 from affecting the other, as does a further capacitor, 19, with respect to output amplifier 12 and volume control 16. Another capacitor shown in dashed lines of short dashes could be used for this purpose between volume control 16 and preliminary amplifier 11.
Such hearing aid devices have been continually reduced in geometrical volume and electrical power drain over the years. Currently, many hearing aids are sufficiently small so as to be housed using in-the-canal packaging to permit the resulting unit to be fitted into human ear canals. Achieving this small a housing for a hearing aid has required microphone 10, speaker or receiver 13, batteries and the electronic circuitry therein to have undergone varied but quite substantial size reductions over those of earlier implementations.
Nevertheless, further reductions in the physical size of these various components of hearing aids are desirable to increase the user's benefits in use thereof. One difficulty with reducing the geometrical volume is the presence of on/off switch 17 shown ganged to volume control 16 in the hearing aid as is very often done since turning down the volume to zero at which point electrical power drain also ceases seems natural, intuitive and convenient to users. Switch contacts from a volume control require a certain spatial volume and are usually made as small as possible, a situation which results in rather small metal parts that are vulnerable to breakage during use. In addition, such small switches are relatively costly to make. Thus, there is a desire to provide circuit arrangements, such as for hearing aids, which can minimize power drain without the use of added small mechanical parts, some of which are moveable, beyond use of an amplitude control, or volume control, potentiometer.